This is a replacement tail drive belt for the Align 600 and 600CF line of helicotpers. It is a 592 tooth XL pitch belt and runs inside the tail boom driven by the tail drive gear and transmits the power to the tail rotor shaft assembly. Careful adjustment of the belt tension is required for optimum performance. Having the belt too tight can cause excessive power consumption while running it too loose can cause slipping and premature wear to the belt and pulleys.